Prevention of cadmium-induced effects on regional glutathione status of rat brain by vitamin E

Disruption of essential metal homeostasis in the brain by cadmium and high-fat diet

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Whole-life exposure to cadmium leads to elevated metal levels in the brain that further increases in high-fat diet fed mice.

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Female animals accumulate more cadmium in the brain than males, under all treatment conditions.

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Cadmium exposure is associated with changes in the levels of several essential metals.

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Cadmium and high fat diet increase levels of superoxide anion in the cortex, amygdala and hippocampus.

Analyses of human cohort data support the roles of cadmium and obesity in the development of several neurocognitive disorders. To explore the effects of cadmium exposure in the brain, mice were subjected to whole life oral cadmium exposure. There were significant increases in cadmium levels with female animals accumulating more metal than males (p < 0.001). Both genders fed a high fat diet showed significant increases in cadmium levels compared to low fat diet fed mice (p < 0.001). Cadmium and high fat diet significantly affected the levels of several essential metals, including magnesium, potassium, chromium, iron, cobalt, copper, zinc and selenium. Additionally, these treatments resulted in increased superoxide levels within the cortex, amygdala and hippocampus. These findings support a model where cadmium and high fat diet affect the levels of redox-active, essential metal homeostasis. This phenomenon may contribute to the underlying mechanism(s) responsible for the development of neurocognitive disorders.

Arsenic-induced oxidative stress and its reversibility

This review summarizes the literature describing the molecular mechanisms of arsenic-induced oxidative stress, its relevant biomarkers, and its relation to various diseases, including preventive and therapeutic strategies. Arsenic alters multiple cellular pathways including expression of growth factors, suppression of cell cycle checkpoint proteins, promotion of and resistance to apoptosis, inhibition of DNA repair, alterations in DNA methylation, decreased immunosurveillance, and increased oxidative stress, by disturbing the pro/antioxidant balance. These alterations play prominent roles in disease manifestation, such as carcinogenicity, genotoxicity, diabetes, cardiovascular and nervous systems disorders. The exact molecular and cellular mechanisms involved in arsenic toxicity are rather unrevealed. Arsenic alters cellular glutathione levels either by utilizing this electron donor for the conversion of pentavalent to trivalent arsenicals or directly binding with it or by oxidizing glutathione via arsenic-induced free radical generation. Arsenic forms oxygen-based radicals (OH(•), O(2)(•-)) under physiological conditions by directly binding with critical thiols. As a carcinogen, it acts through epigenetic mechanisms rather than as a classical mutagen. The carcinogenic potential of arsenic may be attributed to activation of redox-sensitive transcription factors and other signaling pathways involving nuclear factor κB, activator protein-1, and p53. Modulation of cellular thiols for protection against reactive oxygen species has been used as a therapeutic strategy against arsenic. N-acetylcysteine, α-lipoic acid, vitamin E, quercetin, and a few herbal extracts show prophylactic activity against the majority of arsenic-mediated injuries in both in vitro and in vivo models. This review also updates the reader on recent advances in chelation therapy and newer therapeutic strategies suggested to treat arsenic-induced oxidative damage.

Chronic arsenic poisoning in the rat: treatment with combined administration of succimers and an antioxidant

The influence of the coadministration of vitamin C or vitamin E on the efficacy of two thiol chelators, meso-2,3-dimercaptosuccinic acid (DMSA) or monoisoamyl DMSA, in counteracting chronic arsenic toxicity was investigated in rats. Vitamin C and vitamin E were only mildly effective when given alone or in combination with the above chelators in mobilizing arsenic from the target tissues. However, combined administration of vitamin C plus DMSA and vitamin E plus MiADMSA led to a more pronounced depletion of brain arsenic. The supplementation of vitamins was significantly effective in restoring inhibition of blood delta-aminolevulinic acid dehydratase (ALAD) oxidative stress in liver, kidneys, and brain as reflected by reduced levels of thiobarbituric acid reactive substance and oxidized and reduced glutathione levels. The results thus lead us to suggest that coadministration of vitamin E or vitamin C may be useful in the restoration of altered biochemical variables (particularly the effects on heme biosynthesis and oxidative injury) although it has only a limited role in depleting arsenic burden.

Nomega-nitro-L-arginine, a nitric oxide synthase inhibitor, antagonizes quinolinic acid-induced neurotoxicity and oxidative stress in rat striatal slices

Nitric oxide (NO) is a potential contributor to neurotoxicity following overactivation of N-methyl-D-aspartate (NMDA) receptors. In this work we investigated the effect of Nomega-nitro-L-arginine (L-NARG 25, 50, or 100 microM), a selective inhibitor of nitric oxide synthase (NOS) -the synthetic enzyme of NO- on quinolinic acid (QUIN 100 microM)-induced neurotoxicity (measured as lactate dehydrogenase (LDH) leakage) in rat striatal slices. Oxidative stress was also measured both as lipid peroxidation and as the levels of reduced (GSH) and oxidized (GSSG) glutathione, in an effort to elucidate a possible participation of NO in the toxic mechanisms involved in NMDA receptor-mediated neuronal injury. The action of L-arginine (L-ARG 100 or 200 microM), a well-known NO precursor, was also tested on QUIN-induced neurotoxicity and oxidative stress. Results showed that QUIN produced significant changes in both cell damage (177%) and oxidative injury (203% in lipid peroxidation, 68% in GSH, and 123% in GSSG) as compared to control values. All these effects were antagonized by adding L-NARG to the incubation media, whereas L-ARG alone, or in combination with QUIN, significantly enhanced both lipid peroxidation and LDH leakage. Moreover, the protective effects of L-NARG on QUIN-induced lipid peroxidation were reversed by addition of an excess of L-ARG to the media. These findings indicate that NO is probably mediating the mechanism of neurotoxicity produced by QUIN, which may be of potential value to explain the molecular basis of neurodegenerative processes linked to QUIN-mediated NMDA receptor overactivation.

Cadmium induced thyroid dysfunction in chicken: hepatic type I iodothyronine 5'-monodeiodinase activity and role of lipid peroxidation

Administration of cadmium chloride (2.5 mg/kg body weight/day) to chickens daily for 15 days decreased serum triiodothyronine (T3) concentration (by 68.75%) without altering the levels of serum thyroxine (T4). Hepatic 5'-monodeiodinase (5'D-I) and superoxide dismutase (SOD) activities were also decreased (by 90.47% and 20.81% respectively) with a concomitant increase in lipid peroxidation (LPO, by 206.25%). Administration of the antioxidant vitamin E (alpha-tocopherol, 5 mg/kg body weight on alternate days) to cadmium intoxicated chickens restored thyroid function by maintaining normal hepatic 5'D-I activity and serum thyroid hormone concentrations. It also prevented cadmium-induced increase in LPO. We conclude that the metal-induced inhibition in hepatic 5'D-I activity is mediated through LPO.

Effect of melatonin on cadmium-induced hepatotoxicity in male Sprague-Dawley rats

Effect of melatonin on toxicity of cadmium (Cd) was studied in male SD rats co-administered daily Cd (1 mg/kg b.w., s.c.) with melatonin (10 mg/kg b.w., i.p.) for 15 days. Cd alone injection decreased GSH concentrations in the liver and RBC by 35% and 43% compared with those in saline-treatment group, but not in the kidney and whole brain. The activity of GSSG-reductase was significantly decreased in the liver of Cd alone injected rats, while melatonin given in combination with Cd failed to prevent the Cd-induced decreased activity of hepatic GSSG-reductase. However, the hepatic GSH concentration decreased by Cd alone was restored by melatonin treatment, and the melatonin also ameliorated Cd-induced histopathological changes in the liver. Therefore, data indicate that melatonin restores the reduction of hepatic GSH level induced with Cd regardless of GSSG-reductase activity, and suggests that melatonin may ameliorate Cd-induced hepatotoxicity.

Protective effects of vitamin E against lead-induced deterioration of membrane associated type-I iodothyronine 5'-monodeiodinase (5'D-I) activity in male mice

The protective role of vitamin E (vit E) on lead-induced thyroid dysfunction with special reference to type-I iodothyronine 5'-monodeiodinase (5'D-I) activity in mice liver was investigated. Daily intraperitoneal (i.p.) injection of lead acetate (0.5 mg/kg body weight) for 30 days significantly decreased serum 3,3',5-triiodothyronine (T3) concentration and hepatic 5'D-I activity. Furthermore, lead significantly increased peroxidative reactions involving membrane components (lipid peroxidation, LPO) while the activities of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) were decreased in mouse liver. Simultaneous administration of vit E (5 mg/kg body weight) and 0.5 mg/kg body weight of lead restored thyroid function in mice by maintaining normal hepatic 5'D-I activity and serum thyroid hormone concentrations. It also prevented increase in LPO and inhibition of SOD and CAT activities in liver. We suggest that the intact membrane structure is a must for 5'D-I activity and the administration of vit E may prevent the lead induced thyroid dysfunction by maintaining membrane architecture.

Development of brain free radical scavenging system and lipid peroxidation under the influence of gestational and lactational cadmium exposure

1. Rat pups were exposed to cadmium (Cd) gestationally and lactationally through mothers receiving 20 ppm Cd in drinking water, ad libitum, from zero day of pregnancy. 2. The sequential measurement of brain lipid peroxidation showed an increase in thiobarbituric acid reactive substances at 1 (73%), 7 (30%), 14 (22%) and 21 (354%) days of age compared to respective controls. 3. A marked variation in reduced glutathione levels was observed at different postnatal ages of both control and Cd-treated groups. The levels of brain total sulphydryls were increased significantly in experimental animals at 1 (30%) and 7 (12%) days of age. 4. Cd exposure increased the activities of superoxide dismutase and glutathione peroxidase by 45% and 104%, respectively, at day one. However, the continuous exposure inhibited them at 7, 14 and 21 postnatal days. 5. Cadmium treatment elevated the levels of brain catalase and glutathione reductase at all the studied ages with a maximum alteration of 66% and 50%, respectively, at 21 days of age. 6. The data indicate that the exposure of pregnant mothers to low doses of Cd produced changes in the brain antioxidant defence mechanisms at critical periods of development which may have serious implications in later life.

Oxygen radicals: common mediators of neurotoxicity

The inherent biochemical, anatomical and physiological characteristics of the brain make it especially vulnerable to insult. Specifically, some of these characteristics such as myelin and a high energy requirement provide for the introduction of free radical-induced insult. Recently, the biochemistry of free radicals has received considerable attention. It also has become increasingly apparent that many drug and chemical-induced toxicities may be evoked via free radicals and oxidative stress. Major points addressed in this work are the regulation of neural free radical generation by antioxidants and protective enzymes, xenobiotic-induced disruption of cerebral redox status, and specific examples of neurotoxic agent-induced alterations in free radical production as measured by the fluorescent probe dichlorofluorescein. This article considers the thesis that free radical mechanisms may contribute significantly to the properties of several diverse neurotoxic agents and proposes that excess production of free radicals may be common phenomena of neurotoxicity.

Cadmium toxicity: unique cytoprotective properties of alpha tocopheryl succinate in hepatocytes

Rat hepatocyte suspensions were exposed to toxic concentrations of cadmium (Cd) in the presence and absence of unesterified alpha-tocopherol (T) or alpha-tocopheryl succinate (TS). The exogenous administration of TS completely protected hepatocytes from Cd-induced injury and lipid peroxidation. However, hepatocytes exposed to T were not protected from the toxic manifestations of cadmium even though this treatment resulted in a rapid marked accumulation of cellular T. The rate of cadmium uptake by hepatocytes was not significantly altered by exogenous TS or T treatment. These studies indicate that TS cytoprotection against Cd toxicity results not from alterations in Cd uptake or the accumulation of T but rather from the cellular presence of the intact TS molecule. The data also indicate that the depletion of cellular T is not the critical cellular event that is responsible for Cd-induced injury. Instead it appears that TS possess unique cytoprotective properties that intervene in the critical cellular events that lead to Cd toxicity. Thus, TS administration represents a promising new strategy for the mechanistic study and prevention of tissue damage resulting from Cd exposure.

Prevention of chemically induced changes in synaptosomal membrane order by ganglioside GM1 and alpha-tocopherol

Synaptosomal membrane order has been studied by analysis of light depolarization by fluorescent dyes intercalated within membranes following exposure to various environmental toxicants. Two probes were explored: 1,6-diphenyl-1,3,5-hexatriene (DPH), signaling predominantly from the lipid-rich membrane core, and 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH), reporting from the more hydrophilic membrane surface. Chlordecone, a neurotoxic insecticide, decreased the anisotropy of either dye and this change could be prevented by prior treatment of synaptosomes with ganglioside GM1 but not alpha-tocopherol. Exposure to an iron-ascorbic acid oxidizing mixture enhanced synaptosomal membrane order and this effect was blocked by preincubation with alpha-tocopherol but not ganglioside GM1. While these interactions may have partially reflected additive anisotropy changes, the protective agents were also effective at concentrations where they did not in themselves modulate membrane order. Methyl mercuric chloride at concentrations up to 100 microM had no discernable effect upon membrane order. It is suggested that these changes in membrane order may underlie some of the previously reported variations in the content of ionic calcium and in the leakiness of synaptosomes.